The present invention relates to glitter having desirable and/or unique optical characteristics.
Glitter, which is a plurality of particles (i.e., a pieces or fragments of a material) having a regular or irregular periphery, is known in forms that include light reflecting or light refracting material (see, e.g., U.S. Pat. Nos. RE 31,780 (Cooper et al.), U.S. Pat. No. 3,764,067 (Coffey et al.), U.S. Pat. No. 4,310,584 (Cooper et al.), and U.S. Pat. No. 5,294,657 (Melendy et al.)). Materials useful as glitter include particles of metal (e.g., aluminum, copper, silver, gold, and brass), particles of transparent or colored, solid organic materials (e.g., poly(ethylene terephthalate), polymethacrylate, and poly(vinylbutyral)), and particles of metal coated film or paper (e.g., aluminum coated poly(ethylene terephthalate) film). Glitter may be clear and/or be provided in a variety of colors (e.g., silver, gold, blue, red, etc.), or mixtures thereof; and may be provided in a variety of shapes (e.g., circles, squares, rectangles, triangles, diamonds, stars, symbols, alphanumerics (i.e., letters and/or numbers), or mixtures of different shapes.
Glitter may be used in loose form (i.e., non-agglomerated, flowable) adhered to or embedded in a solid material, or dispersed in a liquid. In loose form, for example, glitter may be thrown into the air to create a decorative visual display during a festive occasion, such as a party or parade, or spinkled onto a surface (including hair). In another aspect, glitter is commonly adhered to the surface of, or embedded in, articles (e.g., jewelry, clothing, toys and novelties, art work, and ornaments) to enhance their visual appearance. Glitter is also dispersed in a liquid to provide a visual effect (e.g., globes having a winter scene with simulated snow flakes), or to enhance the appearance of a coating (e.g., paints (e.g., automotive paints and hobby paints), glue, and fingernail polish).
Metallic glitter, which is the among the most reflective types of glitter, is frequently preferred for a variety of end uses. The use of metallic glitter is not, however, without disadvantage. Some reflective metals used in glitter such as silver and gold are relatively expensive. Others, such as copper or aluminum may corrode or oxidize when exposed to air and/or water. Hence, metal containing glitters are relatively expensive, due to the inherent cost of the metal and/or because they require the addition of a protective coating which increases the cost and complexity of producing the glitter. In addition, solid metal glitters (i.e., glitter comprising solid particles or flakes of metal) may abrade equipment (e.g., spray guns, mixers, and extruders) used in the manufacture glitter or glitter-containing products. Further, solid metal glitters have a higher specific gravity than typical coating formulations, thus causing the glitter to settle to the bottom of the coating container.
Conventional plastic glitters avoid some of the infirmities associated with metal glitters, but have additional infirmities of their own. Thus, many prior art plastic glitters, especially those based on absorbing dyes or pigments, exhibit reflectivities that are much lower than those observed with metallic glitters. Other plastic glitters are unavailable in certain colors, due to the inflexibility of their method of manufacture. Still other plastic glitters reflect light in a primarily diffuse (as opposed to specular) manner. These features, alone or in combination, result in a glitter that lacks vibrancy and is not eye-catching.
There is thus a need in the art for a plastic glitter or glitter composition that is inexpensive, highly reflective, available in a wide variety of colors, and catching to the eye. These and other needs are met by the glitters of the present invention, as hereinafter described.
The present invention provides glitter (particles) comprising color shifting film which comprises alternating layers of at least a first and second polymeric material, wherein at least one of the first or second polymeric materials is birefringent, wherein the difference in indices of refraction of the first and second polymeric materials for visible light polarized along first and second axes in the plane of the layers is at least about 0.05, and wherein the difference in indices of refraction of the first and second polymeric materials for visible light polarized along a third axis mutually orthogonal to the first and second axes is less than about 0.05. Preferably, the color shifting film has at least one transmission band in the visible region of the spectrum and at least one reflection band (preferably having a peak reflectivity of at least about 70%, more preferably, at least 85%, even more preferably, at least 95%) in the visible region of the spectrum.
In another aspect, preferably at least one of the first or second polymeric materials of the color shifting film is positively or negatively birefringent. In another aspect, preferably the difference in indices of refraction of the first and second polymeric materials for visible light polarized along first and second axes in the plane of the layers is xcex94x and xcex94y, respectively, wherein the difference in indices of refraction of the first and second polymeric materials for visible light polarized along a third axis mutually orthogonal to the first and second axes is xcex94z, and wherein the absolute value of xcex94z is less than about one half (in some embodiments one quarter, or even one tenth) the larger of the absolute value of xcex94x and the absolute value of xcex94y.
Further with regard to the color shifting film, at least one of the first and second materials can be a strain hardening polyester (e.g., a naphthalene dicarboxylic acid polyester or a methacrylic acid polyester). In other aspect, the first polymeric material can be polyethylene naphthalate and the second polymeric material polymethylmethacrylate.
Glitter according to the present invention may be in any of a variety of desired shapes (e.g., circles, squares, rectangles, triangles, diamonds, stars, alphanumerics, symbols, characters, (e.g., comic, television, movie, etc.), other polygons (e.g., hexagons), and mixtures of at least two different shapes) and sizes (including mixtures of two or more different sizes). Typically, at least a portion of the glitter has particle sizes (i.e., maximum particle dimension) of up to about 1.25 cm (0.5 inch) more typically less than about 10 mm, or even less than about 3 mm. In another aspect, at least a portion of the glitter typically has particle sizes ranging from about 50 micrometers to about 3 mm; for some uses preferably from about 100 micrometers to about 3 mm. Larger particle sizes (i.e., up to about 1.25 cm (0.5 inch)) of glitter according to the present invention may be preferred for use as confetti.
In another aspect, the thickness of the color shifting film comprising glitter according to the present invention is typically less than about 125 micrometers, more typically less than 75 micrometer, and preferably less than 50 micrometers. For some applications, such as paint (e.g., automotive paints), thickness of even 15 micrometers may also be useful. In another aspect, the thickness of the film is selected such that it is less than or equal to 25% of the minimum planar dimension of the glitter particle formed from the film. For example, for a circular glitter particle having a diameter of about 1 mm, the preferred film thickness would be less than or equal to 0.25 mm.
Glitter according to the present invention may be used or provided in any of a variety ways, including in loose form, attached to the surface of a substrate, in a dispersible combination, or present in a matrix material ranging, for example, from liquids, such as water and alcohols, to gels, such as silicone and glycerol, to hard, rigid materials such as plastics, particle board, and fiberglass. Examples of other matrix materials include putties or molding clays, rubbers, adhesives (e.g., glue sticks), crayons, and paper and cardboard.
In one embodiment wherein the glitter is incorporated into a matrix material (e.g., a cross-linked polymeric material), a composite article comprises glitter according to the present invention dispersed (e.g., uniformly or non-uniformly) within a translucent (including transparent) matrix material. In another embodiment wherein the glitter is incorporated into a matrix material, a composite article comprises glitter according to the present invention dispersed within a matrix material, wherein at least a portion of the glitter according to the present invention is observable by a viewer of the composite material comprising the matrix material and the glitter. In the latter example, the matrix material need not be translucent (i.e., can be opaque) provided that glitter is at the outer surface of the matrix material such that at least a portion of the glitter according to the present invention is observable by a viewer of the article.
In another aspect, the present invention provides an article or composition comprising a substrate, a matrix disposed on the substrate, and a plurality of glitter according to the present invention disposed in the matrix.
Articles incorporating glitter according to the present invention may, for example, have the glitter uniformly or non-uniformly (including randomly) dispersed therein and/or thereon, as well have some areas with the glitter uniformly or non-uniformly dispersed therein and/or thereon, and other areas wherein it is non-uniformly or uniformly, respectively, dispersed therein and/or thereon. Further, the glitter may be present such that there are concentration gradients of glitter.
Glitter according to the present invention can be used, for example, to interact with electromagnetic radiation (e.g., visible light) to create desirable, interesting, and/or unique visual effects.
Certain preferred color shifting films used in the present invention are advantageous over prior art color films in many respects. For example, while color shifting films based on isotropic materials are known, these preferred films exhibit decreased reflectivities at non-normal angles of incidence, which diminishes the intensity of the reflected wavelengths at non-normal angles of incidence. Hence, such films appear lighter and have less colors at oblique angles. Other color shifting films change their spectral profile as a function of angle, resulting in diminished color purity and/or less dramatic color shifts with angle. Another advantage is unlike metal based reflectors, for example, multilayer optical films do not tarnish in water or high humidity conditions.
Glitter converted from color shifting film has unusually visually pleasing properties when viewed xe2x80x9cin the flopxe2x80x9d (i.e., when viewed at such an angle that the specular reflection is not causing a glint or a sparkle). In the flop, color shifting film glitter simply gives the normal color shift that the film itself would provide (i.e., the glitter still looks colorful and appealing). Other glitters, especially metallic glitters, in the flop look dark thereby giving a dirty appearance.